# nearbyint, nearbyintf, nearbyintl

From cppreference.com
< c‎ | numeric‎ | math

Defined in header ``<math.h>`` |  |
float nearbyintf( float arg ); | (1) | (since C99)
double nearbyint( double arg ); | (2) | (since C99)
long double nearbyintl( long double arg ); | (3) | (since C99)
Defined in header ``<tgmath.h>`` |  |
#define nearbyint( arg ) | (4) | (since C99)

1-3) Rounds the floating-point argument arg to an integer value in floating-point format, using the current rounding mode.
4) Type-generic macro: If arg has type long double, `nearbyintl` is called. Otherwise, if arg has integer type or the type double, `nearbyint` is called. Otherwise, `nearbyintf` is called, respectively.

### Parameters

arg | - | floating-point value

### Return value

The nearest integer value to arg, according to the current rounding mode, is returned.

### Error handling

This function is not subject to any of the errors specified in `math_errhandling`.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- FE_INEXACT is never raised.
- If arg is ±∞, it is returned, unmodified.
- If arg is ±0, it is returned, unmodified.
- If arg is NaN, NaN is returned.

### Notes

The only difference between `nearbyint` and rint is that `nearbyint` never raises FE_INEXACT.

The largest representable floating-point values are exact integers in all standard floating-point formats, so `nearbyint` never overflows on its own; however the result may overflow any integer type (including intmax_t), when stored in an integer variable.

If the current rounding mode is FE_TONEAREST, this function rounds to even in halfway cases (like rint, but unlike round).

### Example

Run this code

    #include <fenv.h>
    #include <math.h>
    #include <stdio.h>

    int main(void)
    {
    // #pragma STDC FENV_ACCESS ON
        fesetround(FE_TONEAREST);
        printf("rounding to nearest:\nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
        printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
        printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
        printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
        printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
        printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));

        fesetround(FE_DOWNWARD);
        printf("rounding down: \nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
        printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
        printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
        printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
        printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
        printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));

        printf("nearbyint(-0.0) = %+.1f\n", nearbyint(-0.0));
        printf("nearbyint(-Inf) = %+.1f\n", nearbyint(-INFINITY));
    }

Output:

    rounding to nearest:
    nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +4.0
    nearbyint(-2.3) = -2.0  nearbyint(-2.5) = -2.0  nearbyint(-3.5) = -4.0
    rounding down:
    nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +3.0
    nearbyint(-2.3) = -3.0  nearbyint(-2.5) = -3.0  nearbyint(-3.5) = -4.0
    nearbyint(-0.0) = -0.0
    nearbyint(-Inf) = -inf

### References

- C23 standard (ISO/IEC 9899:2024):

  - 7.12.9.3 The nearbyint functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.6.3 The nearbyint functions (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.12.9.3 The nearbyint functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.6.3 The nearbyint functions (p: TBD)

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.9.3 The nearbyint functions (p: 251-252)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.6.3 The nearbyint functions (p: 526)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.9.3 The nearbyint functions (p: 232)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.6.3 The nearbyint functions (p: 463)

### See also

rintrintfrintllrintlrintflrintlllrintllrintfllrintl (C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99) | rounds to an integer using current rounding mode with exception if the result differs (function)
roundroundfroundllroundlroundflroundlllroundllroundfllroundl (C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99) | rounds to nearest integer, rounding away from zero in halfway cases (function)
fegetroundfesetround (C99)(C99) | gets or sets rounding direction (function)
C++ documentation for nearbyint

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